Weighing scale



Feb. 4, 1936. s. N. HURT WEIGHING SCALE Filed Feb. '2, 1955 2Sheets-Sheet 1 Samue/ Hur;

INVENTOR ATTORNEY Feb. 4, 1936.

S. N. HURT WEIGHING SCALE Filed Feb. 2, 1935 2 Sheets-Sheet 2Somue/A/Hurt INVENTOR ATi'ORNEY Patented Feb. 4, 1936 UNITED STATESPATENT OFFICE WEIGI-IING SCALE Application February 2, 1935, Serial No.4.618

7 Claims.

This invention relates to weighing scales, and particularly to weighingscales in which load counter-balancing is accomplished by springs.

In weighing scales of this type the springs ex- 5 pand and become lessstiff with rises in temperature and contract and become more stifi asthe temperature falls.

It is an object of my invention to provide a simple and effective meansfor compensating for such expansion and contraction and change ofstiffness in the load-counterbalancing springs by causing the scaleindicator to remain at zero position notwithstanding such expansion andcontraction and to move equal distances for equal variations in loadnotwithstanding changes in stifiness of the load-counterbalancingsprings.

Other objects and advantages will be apparent from the followingdescription, in which reference is had to the accompanying drawingsillustrating a preferred embodiment of my invention and wherein similarreference numerals designate similar parts throughout the several views.

In the drawings:

Figure I is a rear elevational view of a loadcounterbalancing mechanismembodying my invention, and the framework supporting same, the rearcover of the frameworkbeing removed and parts being broken away to moreclearly disclose the mechanism;

; Figure II is a view showing diagrammatically the mechanism in no load"position;

Figure III is a view showing diagrammatically the mechanism in theposition assumed by it under load; and

5 Figure IV is a detail fragmentary view showing a modification of amanually operable zero adjusting device which may be employed in themechanism of my invention.

The invention is illustrated as embodied in a L0 'dial scale of thehanging type, though it is equally applicable to other forms of springscales having revoluble indicators.

Referring to the drawings in detail, the framework, which supports theload-counterbalancing t5 mechanism in the form of the deviceillustrated, comprises a hoop-like annulus I having a pair of bars 2 and3 extending diametrically across it at its front and rear edges. Securedto lugs 4 and 5 which project inwardly from the upper 30 part of theannulus l is a curved bar 6, to the center of which is secured an ear Iwhich extends upwardly through an opening in the annulus I and isprovided with an eye 8 to receive a hook (not shown) from which thescale may be 56 511 11 A pair of load-cmmterbelancing hel c l coil prins 9 and II are suspended. y means of hooks formed at their upper ends,from openings I I and I2 formed in the curved bar 6, the lower ends ofthe springs being connected, by means of 5 hooks I3 and I4 adjustablysecured at the lower ends of the springs, to eyes I5 and I5, which, inturn, are secured to .a. transversely extending channel-shaped equalizerII, a load-supporting bar III being pivotally connected at its upper end10 to the equalizer I] midway between the eyes I5 and I6 and having itslower end, which projects through an opening in the lower side of theannulus I, provided with an eye I9 to which the ball of a load-receivingpan (not shown) may be connected.

The equalizer I1 is provided at its ends with upturned ears and 2|, towhich are pivotally connected the lower ends of plunger rods 22 .and'23, the upper ends of the rods 22 and 23 being 20 connected to plungers(not shown) which reciprocate vertically in inverted dashpots 24 and 25,the upper ends of which are provided with lugs 26 and 21. which lugs aresecured to the ends of the curved rod 6 so that the dashpots 24 and are25 supported thereby.

Mounted on the web of the channel-shaped equalizer I] is a block 28 andsecured to the block 28 is one end of .a. laterally extending leafspring 29, to the opposite end of which is pivotally con- 30 nestedastirrup 30, the stirrup 2. being hung from the lower end of a lighthelical spring 3 I, the upper end .of which is connected to a bracket 33mounted for vertical adjustment on the upper part of the annulus I.Pivotally supported on the laterally extending leaf spring 29,intermediate the block 22 .and the stirrup 30, is the lower end of anupwardly extending rack 34 which meshes with a pinion 35 mounted on theshaft 36 which is journaled in hearings in the diagonally extend- 40 ingbars .2 and 3 and to which is fixed the pointer er indicating hand (notshown) of the scale.

A small weight 31, supported on a short arm 38 which is fixed to therack 34, serves to hold the rack with slight pressure in mesh with thepinion, and a guard roller 35, mounted by means of a bracket 4:! on thediagonally extending bar 2, serves to prevent the rack from jumping outof mesh with the pinion when the scale is subjected to shock.

Secured to the block '21 and extending upwardly therefrom is a standard4|, adjacent the top of which is fixed the upper end of a bimetallicthermosensitive element 42. The lower end of the element 42, which ispreferably provided with Fahrenheit.

a chisel edge, engages the upper surface of the leaf spring 29, and thecomposition and structure of the element 42 is such that when thetemperature rises the element 42 bends to move its lower end toward theblock 28 along the upper surface of the leaf spring 29 and when thetemperature falls the element 42 bends in the opposite direction to moveits lower end along the upper surface of the leaf spring 29 away fromthe block 28. The effective length of the leaf spring 29, and hence theextent to which it may be bent by a. given pull of the light spring 3|,is dependent upon the position of the lower end of the thermosensitiveelement 42.

For the purpose of initially adjusting the scale or setting it on zero,an adjusting screw 45 is provided to move the bracket 33 up and down,the bracket 33 being guided in such movements by a lug 45 depending fromthe bar 6. A coil spring 41 surrounds the adjusting screw 45 and servesto take up any looseness which may exist between the threads of thescrew 45 and the threads in the bracket 33.

4 Operation dashpots 24 and 25. As the equalizer moves downwardly itcarries the block 28, leaf spring 29 and rack 34 downwardly also, butthe relatively light spring 3|, as it stretches under the downwardmovement, exerts a small upward pull on .the end of the leaf spring 29,thus bending the leaf spring 29 slightly, so that the downward movementof the rack 34 is slightly less than the downward movement of theequalizer H. The

extent to which the leaf spring 29 is bent during a given downwardmovement depends not only upon the stifiness of the leaf spring 29 andthe pull exerted by the light coil spring 3|, but also upon the positionof the lower end of the thermosensitive element 42. Since the lower endof the element 42 moves toward the block 28 under the influence ofrising temperature, thus lengthening the spring 29, and moves away fromthe block 28 under the influence of a fall in temperature, thusshortening the spring 29, the spring 29 is permitted to bend upwardly toa greater extent when the temperature is high and the springs 9 and Illstretch further under a given load, and when the temperature is loweredand the springs 9 and I0 stretch less under a given load the leaf spring29 is shortened and bends less in response to the pull of the lightspring 3 The length and stiffness of the leaf spring 29, the stiffnessof the light spring 3|, and the structure, composition and length of thethermosensitive element 42 are so proportioned that the rack 34 movesdownwardly equal distances for equal changes in load upon the equalizerat all temperatures at which the scale is intended to operate.Ordinarily the parts are constructed and proportioned to provide forequal movements of they indicator for .equal changes in load at alltemperatures ranging from -10 degrees Fahrenheit to degrees The partsare also so constructed and proportioned that when the equalizer I1 issubjected only to the load imposed by the weight of the drawbar l8 andthat of the bail and pan of the load-receiver, the position of the rack34 remains unchanged during changes in temperature from l0 degreesFahrenheit to +120 degrees Fahrenheit. When the temperature change issuch as to lengthen the load-counterbalancing springs 9 and ID, thelower end of the thermosensitive element 42 moves toward the block 28,thus lengthening and weakening the leaf spring 29, so that it is bentupwardly by the contractile force of the light spring 3|. When theload-counterbalancing springs 9 and I0 shorten with a drop intemperature, the leaf spring 29 is shortened and stiffened and the lightspring 3| is stretched slightly, so that the position of the rack 34remains unchanged.

In a weighing scale embodying this invention which was constructed bythe applicant, the loadcounterbalancing springs 9 and I0 were made tostretch slightly more than three inches under 3|! pounds of load, andtheextent of stretch was found to vary approximately inch when the springswere subjected to variations in temperature ranging from l0 degreesFahrenheit to +120 degrees Fahrenheit. The light coil spring 3| was madeslightly less than one-thirtieth as stifi as the load-counterbalancingsprings; the thermosensitive element 42 was .so proportioned that theposition of its lower end changed onequarter of an inch when the elementwas subj ected to temperature variations ranging from -10 degreesFahrenheit to +120 degrees Fahrenheit and the leaf spring 29 was soproportioned that when a load of 30 pounds was placed upon the scale thepull of the light spring would flex the leaf spring at the point ofattachment of the rack 1 inch more at +120 degrees Fahrenheit than at 10degrees Fahrenheit, thus compensating for the increased stretch in theload-counterbalancing springs and causing the rack to move the samedistance for a given load at 120 degrees Fahrenheit as at l0 degreesFahrenheit.

To set the indicator on zero for the purpose of compensating for changesin weight of the loadreceiver, etc., the adjusting screw 45 is turned tomove the bracket 33 up or down, thus lifting or lowering the lightspring 3|, and consequently lifting or lowering the rack 34. Theadjusting device shown in Figure I is accessible from the top of thescale. In Figure IV is illustrated a modification which makes theadjusting device accessible from the lower side of the scale. In themodification shown in Figure IV the spring 3|a is supported by a loop32a hung from one end of a lever 50a fulcrumed on 2. lug secured to theannulus la. The other end of the lever 50a is connected, by means of arod 5|a, to a bracket 33a mounted for vertical adjustment on the lowerside of the annulus Ia. Adjusting the bracket 33a upwardly lowers thespring 3|a and the rack, and adjusting the bracket 33a downwardly raisesthe spring 3|a and the rack. The annulus la is provided with an opening,as at 53, through which the adjusting screw 45 may be reached by ascrewdriver.

Thermosensitive elements similar to the thermosensitive element 42 havebeen arranged to vary the length of leaf springs which supportload-counterbalancing springs. Very great forces are exerted upon suchprior art thermosensitive elements by the leaf spring, to which theentire load is applied, and such forces tend to prevent proper action ofthe thermosensitive devices and to force them out of position. Incontrast to such prior art devices, in the device of my invention theforce exerted upon the thermosensitive device is very slight and has notendency to prevent the thermosensitive device from operatingeffectively or to push it out of position.

The embodiment of my invention herein shown and described is to beregarded as illustrative only, and it is to be understood that theinvention is susceptible to variation, modification and change withinthe spirit and scope of the subjoined claims.

Having described my invention, I claim:

1. In a device of the class described, in combination, springload-counterbalancing means, indicator-operating means, resilient meansconnecting said load-counterbalancing means and said indicator-operatingmeans, means for flexing said resilient connecting means uponapplication of a load to said load-counterbalancing means, and means forcontrolling the extent of flexure of said resilient means to compensatefor effects of changes in temperature upon said load-counterbalancingmeans.

2. In a device of the class described, in combination, springload-counterbalancing means, load-supporting means supported by saidspring load-counterbalancing means, a flexible member carried by saidload-supporting means, indicator- 'ried by said load-supporting means,indicatoroperating means carried by said leaf spring, a relatively lightspring, means connecting said relatively light spring and said leafspring whereby said leaf spring is flexed by movement of saidload-supporting means to reduce movement of said indicator-operatingmeans, and thermosensitive means for varying the flexibility of saidleaf spring.

4. In a device of the class described, in combination, springload-counterbalancing means, load-supporting means supported by saidspring load-counterbalancing means, aleaf spring carried by saidload-supporting means, indicator-operating means carried by said leafspring, a relatively light spring, means connecting said relativelylight spring and said leaf spring whereby said leaf spring is flexed bymovement of said loadsupporting means to reduce movement of saidindicator-operating means, and thermosensitive means for varying theflexibility of said leaf spring, said thermosensitive means acting toincrease the flexibility of said leaf spring with rising temperature anddecrease the flexibility of said leaf spring with falling temperature.

5. In a device of the class described, in combination, springload-counterbalancing means, load-supporting means supported by saidloadcounterbalancing means, a leaf spring having one end flxed to saidload-supporting means, indicator-operating means canied by said leafspring, a relatively light spring, means connecting said relativelylight spring to said leaf spring whereby said leaf spring is flexed uponmovement of said load-support to detract from the consequent movement ofsaid indicator-operating mechanism, and thermosensitive means forvarying the effective length ofsald leaf spring.

6. In a device of the class described, in combination, springload-counterbalancing means, load-supporting means supported by saidloadcounterbalancing means, a leaf spring having one end fixed to saidload-supporting means, indicator-operating means carried by said leafspring, a relatively light spring, means connecting said relativelylight spring to said leaf spring whereby said leaf spring is flexed uponmovement of said load support to detract from the consequent movement ofsaid indicator-operating mechanism, and thermosensitive means forvarying the effective length of said leaf spring, said thermosensitivemeans acting to effectively lengthen said leaf spring with risingtemperature and to effectively shorten said leaf spring with fallingtemperature.

7. In a device of the class described, in combination, a pair of helicalload-counterbalancing springs, an equalizer supported thereby, means forsupporting a load from said equalizer, a horizontally extending leafspring having one of its ends fixed to said equalizer, a relativelylight helical spring, means connecting said relatively light helicalspring to the other end of said leaf spring whereby said leaf spring isflexed upon movement of said equalizer, a rack carried by said leafspring intermediate its ends, and a thermosensitive element flxed tosaid equalizer, said thermosensitive element engaging said leaf springto vary its effective length in response to changes in temperature.

SAMUEL N. HURT.

